1. Field of the Invention
The invention relates generally to a head for recording/reading optical data and method of manufacturing the same, and more particularly to, a head for recording/reading optical data and method of manufacturing the same capable of improving throughput of a laser beam passing through apertures in order to record/read data in a probe type mode (AFM mode) (Atomic Force Microscopy) and a NSOM (Near-Field Scanning Optical Microscopy) mode.
2. Description of the Prior Art
In order to store more information per unit area in an optical storage device, it is required that the wavelength of a recording optical source be reduced or the numerical aperture of a condensing lens must be increased. To satisfy such a requirement, it may be considered to develop a blue laser diode (LD) and to increase the numeral aperture up to 1.0. In these cases, however, there is a limit that information is recorded with a high density due to diffraction of light, in a next generation information storage device requiring a high-density recording.
As an option for overcoming this limit, there are a SPR (Scanning Probe Recording) technology using a probe of AFM (Atomic Force Microscope), an ultra-resolution medium technology, a technology using a Near-Field Scanning Optical Microscopy (NSOM) probe that overcomes the diffraction limit of light and the like.
As a first example of a prior art, a technology using a NSOM optical fiber probe employs a laser light outputted to an aperture having a very small size (aperture: several dozens˜several hundreds of nm). In case of the NSOM optical fiber probe, however, it is mechanically very fragile and is not easy to arrange it in plurality at a time. Further, as throughput of light outputted to the aperture is very small (generally about 10−5˜10−7 in cases of an aperture having 100 nm in size), the NSOM optical fiber probe is very difficult to be actually used in view of recording and data processing speed.
In other words, in order to use the NSOM optical fiber probe in an optical storage device, an aperture having a high throughput is required and a probe arranged in plurality and not easily abraded mechanically is required.
A second example of a prior art has a probe having a plurality of apertures through a semiconductor process (FIG. 1).
Referring now to FIG. 1, there are formed a plurality of holders 11 are provided. Probes 12 formed of a thin metal film are formed at the bottom of the holders 11. Apertures 13 are formed between the probes 12. Even in this case, however, as transmissivity of a laser beam outputted from the apertures 13 of the probes 12 is below 10−5 as in conventional optical fiber probe, it is required that transmissivity be increased. A method of improving throughput of light transmitted into a hole at an end portion of the probes 12 includes a method of exciting plasmon, a method of minimizing an optical loss region generated from one wavelength size at the end portion, etc.
The third example of a prior art attempted to improve throughput of the aperture by a method of exciting plasmon. Plasmon Mode, however, it is difficult to effectively excite plasmon since its exciting efficiency depends on the polarization of an incident beam. In order to more effectively excite plasmon, there is a need for an aperture structure by which plasmon can be effectively excited through a special process.
A fourth example of a prior art include a method of making an aperture structure having a high throughput by making an end portion of the probe minimize an optical loss region. The method of minimizing the optical loss region, that is a method introduced in a conventional optical fiber probe, makes the aperture having a very large cone angle through a multi-step wet etching process. A reflection film for reflecting an incident light is located in a first taper region and a reflection film having a very large cone angle is located in a second taper region, so that the optical loss region can be reduced by maximum. Also, a very small aperture having a probe shape is positioned in a third taper region to form an aperture of high throughput. In this case, however, as the size of the aperture representing an optimum high throughput is defined depending on the first taper region and the aperture is manufactured by a multi-step wet etch process, there is a problem that its manufacturing process is complicated. Further, there is a problem that it could not be applied to an optical storage device of a probe mode since the end portion of the probe is very large.
Meanwhile, a fifth example of a prior art includes a method of manufacturing an aperture of a high throughput using semiconductor process and wet etch process. The method manufactures a probe the end portion of which has a parabolic structure of a very large cone angle through anisotropic etching process to silicon, a low-temperature oxide film formation process, a deposition process of Cr and a wet etching process in order to minimize the optical loss region. In case of this structure, however, as the process of manufacturing the probe including the low-temperature oxide film formation process is complicate, there is a problem that it is difficult to make the end portion of the probe in a parabolic shape.
The conventional arts so far attempted to improve throughput by making an actual object. However, there is a method by which a method similar to a method of manufacturing the aperture having a large cone angle is applied to a semiconductor process conceptually.
Referring now to FIG. 2, a sixth example of a prior art will be explained. A relatively large aperture (1 micron to 2 micron) is formed by a silicon semiconductor process and a reflection film is coated, where this structure corresponds to the first taper region mentioned in the fourth example of a prior art. At this time, a hole having a very small size (60 nm) is formed at the center of the reflection film to form an aperture of a high throughput. At this time, a non-linear thin film is additionally coated on the reflection film and self-focusing being a non-linear characteristic is generated through the nonlinear thin film, thus additionally improving the optical throughput of the aperture.
However, this method includes first forming a reflection film in the first taper region and then forming an aperture in the reflection film to form the aperture of a high throughput. However, this method is almost impossible to be used. The reason is that a mode of light reflected by the reflection film could not be effectively transferred to a mode existing in the aperture using only the first reflection film. Also, in this case, there is a region having a large light loss same to a conventional optical fiber probe. Further, though a thin film for causing self-focusing is additionally coated on the reflection film, there actually occurs no any self-focusing phenomenon. The reason is that the refractive index varies spatially in an already-formed structure since the refractive index is spatially different depending on the non-linear characteristic. Due to this, the difference in the phase delay is spatially generated to change the size and shape of beam, so that the amount of beam can be increased since a defocusing phenomenon not self-focusing can be generated. In other words, as the structure in which the non-linear thin film is coated on the reflection film has a limit to reduce the amount of beam (about one wavelength), throughput of light is not so increased. Further, this structure has a structure in which the end portion of the probe is very flat not a probe shape structure. Therefore, there is a problem that this structure could not be applied to an optical storage device using the probe mode though it could be simultaneously applied to the probe mode and the near-field scanning optical microscopy.